Electrical discharge devices



Feb. 1957 r. M. JACKSON ELECTRIC DISCHARGE DEVICES 2 Sheets-Sheet 1Filed April 7, 1954 Inventor T. M. JACKSON A ttom e y Fe. 5, 1957 T. M.JACKSON 2,780,74?

ELECTRIC DISCHARGE DEVICES Filed April 7, 1954 2 Sheets-Sheet 2 InventorT; M. JACKSON 0% w 9% L3 9v 3 nm QM 3 3 3 Q g w QC Attorney ELECTRICALmscnnnon nEvrcEs Thomas Meir-ion Jackson, London, England, assignor toInternational Standard Electric Corporation, New York, N. Y., acorporation of Delaware Application April 7, 1954, Serial No. 421,501Claims priority, application Great Britain May 19, 1953 Claims. (Cl.313-188) The present invention relates to cold cathode electric glowdischarge tubes and is particularly concerned with the construction ofdirectional cathodes for such tubes.

In certain types of cold cathode electric glow discharge tube, electrodearrangements are provided by means of which it is possible in responseto common input signals, to transfer a glow discharge from one of anarray of discharge gaps to a second gap in the array to one side ratherthan the other, the transfer mechanism depending upon the reduction ofstriking potential of the second gap (due to the discharge at the firstgap) being greater than the corresponding reduction of strikingpotential at the gap on the other side of the first gap. Such tubes aredescribed and claimed in U. S. Patent No. 2,553,585 dated May 22, 1951of G. H. Hough. In the constructions disclosed in that application, thedirection of transfer of the discharge is determined by the shape ofcertain of the cathodes, the essential feature of the cathode shapingbeing that the directional cathodes should each comprise a portion ofconvenient shape, say a fiat rectangle, parallel to a plane anode, atwhich cathode glow is positioned during intervals between successivetransfer signals, together with a further portion of cathode in the formof a narrow ribbon-shaped member, usually referred to as a tail, the endof which is immediately adjacent the discharge gap from which thedischarge is to be transferred onto the first mentioned portion'of thecathode, referred to as the plate portion. During the transfer operationcathode glow commences at the end of the tail, spreads along the tailand then on to the plate. Due, primarily, to the large ratio ofperiphery to surface area of the tail portion as compared with the plateportion of the cathode, the maintaining potential for the anode tocathode-tail portion of the discharge gap is higher than that for theportion anode to cathode-plate. Therefore, once the glow has spread onto the cathodeplate, the discharge at the tail is extinguished and, asstated above, the glow remains on the plate portion but not upon thetail. In the practical embodiments described in the specification of theaforesaid U. S. Patent No. 2,553,585, these directional cathodes wereconstructed from metal strip, a portion of which was bent over parallelto the anode to provide the plate portion while the tail portioncomprised an adjacent part of the strip edge-wise-on to the anode. Thedetailed construction of the complete discharge tube is in large measuredetermined by the particular construction of the directional cathodes.

According to the present invention there is provided a cathode in or fora cold cathode electric glow discharge tube comprising a head portionsymmetrically shaped with respect to a given orientation mounted uponthe end of a support wire and a slender tail portion projecting from andin substantially the same plane as, the head portions and in a directionnormal to said given orientation.

The cathodes may be mounted upon an insulator by passing the supportwire through a hole in the insulator 2,780,747 ?atented Feb. 5, 1957 andfixing a tubular shank about the support wire soas to clamp the cathodeto the insulator. It is preferred that the actual discharge surfaces ofthe cathode should be raised above the cathode support member by adistance of the order of the length of the cathode dark space, for whichpurpose a shoulder of appropriate height may be provided under the headportion of the cathode. An array of such cathodes may conveniently bemounted upon a single insulator and secured within a glass envelope bymeans of lead wires sealed in a glass base at one end and secured insidethe respective said tubular shanks at the other. 7

The invention will be further described with reference to embodimentsthereof shown in the accompanying drawings in which:

Fig. 1 shows in section an elevational view of part of a cathodeassembly according to the invention together with a co-operating anode;

Fig. 2 shows a plan view of the cathode of Fig. 1;

Fig. 3 shows a discharge tube containing an anode and an array ofcathodes according to the invention co-opcrating therewith;

Fig. 4 shows curves illustrating the electrical characteristics of adischarge gap using cathodes according to the present invention; and

Fig. 5 shows various modifications of the construction of the tailportion of the cathode of Fig. 1.

In Figs. 1 and 2 a cathode 1 and part of an adjacent cathode 2 are shownmounted upon an insulator 3 underneath a plane anode 4. The main body ofthe cathode comprises a support wire 5 upon the end of which is formedahead portion 6, and an underlying shoulder 7. As shown in Figs. 1 and2, the head portion 6 takes the form of a disc which, together with theshoulder 7, can be formed in the same manner as the head of a wire nail,which, in fact, the cathode resembles. The shoulder 7 is completelyoverlapped by the periphery 8 of the head portion of the cathode andspaces the head portion above the surface of insulator 3 by a distanceequal to the length of the cathode dark space when a discharge currentcauses the cathode glow on the head portion just to reach to theperiphery. By this means glow is inhibited from spreading to theunder-surface of the head portion and prevents any sputtering of cathodematerial on the surface of the insulator from enlarging in the course ofthe life of the tube, the area of the effective cathode dischargesurface.

A fine wire cathode tail 9 is shown in Fig. 1 secured underneath andbent to lie substantially in the plane of the head portion 6 of cathode1, so as to project towards cathode 2.

The cathodes are secured to the insulator 3 by means of tubular shanks10, surrounding, and welded to, the support wires 5 so as to clamp thecathodes in position in the insulator 3.

The provision of the tubular shanks 10 affords a very convenient meansof mounting a cathode array in a discharge tube envelope, an examplebeing illustrated in Fig. 3, in which the envelope 12 comprises a glassbase 13 through which leads 14 are sealed in conventional manner. Theupper ends of these leads 14, as shown in Fig. 1, are fittted into theends of the respective tubular shanks 10, and welded thereto, asindicated in Fig. 1 at 15. The cathode assembly is thus firmly supportedupon the base 13. The anode 4 can be mounted in an analogous manner uponother of the lead wires 14, of which one identified by the numeral 14',is shown in Fig. l, passing through the insulator 3 and secured to'theanode 4 by means of an eyelet 16 and collar 17.

The tail portion 9 of Figs. 1 and 2 should project to within a distanceequal to the length of the cathode dark space from the periphery of thecathode 2.. During operation, the cathode glow at cathode 2 istransferred to the tail portion 9 of cathode 1 and spreads therealongonto the head portion 6, where it is maintained until the next inputsignal, the glow over. the tail portion being extinguished as soon asthe discharge reaches the head portion. Thus in Figs. 1 and 2 thecathode construction is such as to allow transfer of the glow dischargefrom cathode 2 to cathode 1 via the tail portion 9, and in Fig. 3 theglow may be transferred from cathode to cathode clockwise along thearray of cathodes.

Typical relationship between anode-cathode voltage and cathode currentfor a discharge gap formed as in Fig. 1 by a cathode 1 and anode 4 areindicated in the graphs of Fig. 4. The curve A refers to discharge atthe tail portion alone and the curve B to discharge at the head portionof a cathode having the following essential dimensions:

. Inches Diameter of head portion 6 0.104 Thickness of head portion 60.010 Thickness of shoulder 7 0.005 Diameter of tail 9 0.005 Length oftail (projecting beyond head) 0.120

If discharge be initiated, by means with which we are not immediatelyconcerned, at the end of the cathode tail, the discharge current andanode-cathode voltage are given by the co-ordinates of the point C oncurve A, the anode-cathode voltage being then about 178, and the currentabout 0.1 ma. As the discharge current increases, the anode-cathodevolts increase rapidly until at point D cathode glow completely coversthe tail. Further increase of cathode current involves an increase inanode-cathode voltage without corresponding spread of cathode glow untilthe point B is reached, when the glow transfers to the cathode head andthe operating point to E on curve B. The voltage immediately drops bysome volts, becoming lower than the smallest voltage at which dischargeto the tail can be maintained; the transfer of the discharge from tailto head is thus complete. If the discharge current be now reduced, thedischarge characteristic follows the portion EF of curve B. Withincrease of the discharge, as would normally occur, the characteristicto the right of E on curve B is followed. The curve shows a decrease ofanode-cathode voltage to a minimum value, after which it increases againwith increasing current until, at the point G, the glow covers the uppersurface of the cathode head, and then commences to spread down the sidesof the head until, at H. the glow covers the whole upper surface andside of the head. Due to the small clearance above the insulator 3,further spread of glow below the head is prevented. With still furtherincrease of current, now exceeding the maximum design current, thevoltage continues to rise until at the point I the glow spreads oncemore onto the tail portion 9.

In the manufacture of a cathode assembly according to the invention, wefind it convenient to secure a rather longer length of fine wire than isrequired to form a cathode tail 9 onto the main body of the cathode, andto shape and cut the fine wire to the requiredlength after the severalcathodes have been secured in position on the insulator 3. A spacing jigis positioned beneath the shoulders of two adjacent cathodes, and thecathode tail 9 is bent to the required shape against the jig beforebeing cut off to leave the correct spacing between the tail portion andthe adjacent cathode.

In Fig. l the cathode tail is shown secured beneath the head portion 6of the cathode. Various modifications to this method of fixing are shownin Fig. 5, which depicts part of an array of cathodes, all having somedifferent modifications. Thus the left-hand cathode has its tail 9formed of a straight length of fine wire welded directly to the headportion of the cathode as indicated at 21. -.In the adjacent cathode 22the tail 9 is secured to the shank 10, as indicated at 23, and passesthrough an extension 24 of the aperture in the insulator 3 through whichthe cathode support wire 5 is passed. Cathode 25 has its tail portionwelded at 26 to the shank 10, but taken out through a separate aperture27 in the insulator 3 before being bent over. A further modification isshown to the right of Fig. 5 in which cathode 28 has a tail portionformed from a loop of fine wire, one end of which is welded to the shank10 at 29, and passes through an aperture 30, in similar manner to thearrangement of cathode 22, but the tail, instead of being cut offadjacent the next cathode in the array, is bent to pass through afurther aperture 31 in the insulator 3, and is welded again to the shank10 at 32, thus ensuring that the fine wire is not liable to be displacedfrom its correct position during assembly of the discharge tube orsubsequent transport thereof.

While the present invention has been described with particular referenceto a multi-cathode tube, in which discharge is transferred along anarray of cathodes in one direction, there are circuit applications forwhich the mechanism of the transfer operation is itself valuable, and acathode according to the present invention may usefully be incorporatedin a tube having, for example, only a single pair of discharge gaps.

While the principles of the invention have been described above inconnection with specific embodiments, and particular modificationsthereof, it is to be clearly understood that this description is madeonly by way of example and not as a limitation on the scope of theinvention.

What I claim is:

1. In a cold cathode electric glow discharge tube, a cathode having ahead portion, a support wire on which said head portion is mounted and aslender tail portion projecting from and extending in substantially thesame plane as the head portion, a plane cathode-supporting member andmeans for mounting the head portion above said supporting member by adistance substantially equal to the length of the cathode dark space.

2. A tube according to claim 1 in which the said head portion is a discformed on the said support wire in similar manner to the head of a wirenail.

3. A tube according to claim 1 in which said means comprises a shoulderintegral with the head portion, said shoulder resting on the planesurface of the supporting member, with the periphery of the headcompletely overlapping the shoulder and spaced from the said surface,said supporting member having an aperture through which the support wireprojects.

4. A tube according to claim 3 further comprising a tubular shanksurrounding and secured to the said support wire underneath the saidinsulator member so that the cathode is clamped in position.

5. A tube according to claim 4 in which the said tail portion is astraight length of fine wire secured to the said head portion.

6. A tube according to claim 4 in which the said tail portion is a finewire secured to the underside of the said head portion and is formed toproject parallel to, and spaced from, the said surface.

7. A tube according to claim 4 in which the said tail portion is a finewire secured to the said tubular shank and formed to project parallelto, and spaced from, the said surface.

8. A tube according to claim 4 in which the said tail portion is a finewire projecting through an aperture in the said insulator separate fromthe aperture receiving the said support Wire and is bent at right anglesabove the insulator surface to project parallel thereto and spacedtherefrom.

9. A tube according to claim 4 in which the said tail portion is a finewire loop secured to the said tubular shank and passing throughspaced-apart apertures in the said insulator between which the said finewire is parallel References Cited in the file of this patent to andspaced from the said surface. UNIT 10. A cold cathode electric glowdischarge tube com- ED STATES PATENTS prising an array of cathodesaccording to claim 4 mounted 2,553,535 Hough y 22, 1951 upon a commonsaid insulator, the said array and insulator 5 2,575,372 Townsend 20,1951 being secured to a glass envelope base by means of lead 2,521,313Stelnbefg 1952 wires sealed through the base of the tube envelope and2,627,054 P1011811 et 27, 1953 secured in respective said tubularshanks.

